They are not the same sort of thing

I’ve learnt so much at the edge of sleep,

the mind half-aware, half listening close, 

but still connected, as you might suppose,

to something that consciousness must keep,

a matter that my mind desires to keep,

perhaps a memory of tree or rose,

or a sad fact that’s been struck on the nose,

important but not obviously deep.

The edge of death is quite another thing,

hallucination of dull yellow light 

illuminating something that’s not there.

The vision is not something I could bring 

within a fellow human’s mental sight,

only a place substantial as air.